An exhaust gas sensor having an anticipatory controller may be positioned in an exhaust system of a vehicle to detect an air-fuel ratio of exhaust gas exhausted from an internal combustion engine of the vehicle. The exhaust gas sensor readings may be used to control operation of the internal combustion engine to propel the vehicle.
Degradation of the exhaust gas sensor may cause engine control degradation that may result in increased emissions and/or reduced vehicle drivability. Accordingly, accurate determination of exhaust gas sensor degradation and subsequent adjustments to parameters of the anticipatory controller may reduce the likelihood of engine control based on readings from a degraded exhaust gas sensor. In particular, an exhaust gas sensor may exhibit six discrete types of degradation behavior. The degradation behavior types may be grouped into filter type degradation behaviors and delay type degradation behaviors. Further, the degradation behavior types may either be symmetric or asymmetric around stoichiometry. An exhaust gas sensor exhibiting an asymmetric filter type degradation behavior may have a degraded time constant of the sensor reading in only one transition direction of the air-fuel ratio (e.g., rich-to-lean transition or lean-to-rich transition). In response to sensor degradation, anticipatory controller parameters may be adjusted to maintain stability of the closed-loop system operation.
Previous approaches to adjusting parameters of the anticipatory controller of an exhaust gas sensor, responsive to degraded behavior, include adjusting anticipatory controller gains only in the direction of the degradation. As a result, an engine controller may respond asymmetrically to deliver more or less fuel in the direction of the degradation. This asymmetric operation may cause an increase in CO emissions (lean-to-rich filter) or an increase in NOx (rich-to-lean filter).
The inventors herein have recognized the above issues and identified an approach for adjusting fuel injection to an engine responsive to a modified exhaust oxygen feedback signal from an exhaust gas sensor, the modified exhaust oxygen feedback signal modified by transforming an asymmetric response of the exhaust gas sensor to a modified more symmetric response, for example a modified symmetric response. For example, the asymmetric response may be an asymmetric filter degradation response wherein a response rate of the response is degraded in only one transition direction, or degraded to a greater extent in one direction than another. In one example, transforming the asymmetric response to the modified symmetric response may include filtering a non-degraded portion (e.g., transition direction) of the asymmetric response by an amount based on a time constant of a degraded portion of the asymmetric response. After transforming the asymmetric response, one or more parameters of an anticipatory controller of the exhaust gas sensor may be adjusted based on the modified symmetric response. For example, one or more of a proportional gain, an integral gain, a controller time constant, and a controller time delay may be adjusted and applied in both transition directions of the exhaust gas sensor response. In this way, a technical effect of the anticipatory controller being able to operate symmetrically may be achieved, thereby reducing calibration work of the controller and reducing NOx and CO emissions of the engine.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.